The present invention relates generally to the field if disc drive data storage devices. More specifically, the invention relates to reducing contaminants in a housing of a magnetic disc drive.
Disc drive data storage devices are well known in the industry. Such devices use rigid discs coated with a magnetizable medium for storage of digital information in a plurality of circular concentric tracks. This information is written to and read from the discs using a transducing head mounted on an actuator mechanism which moves the head from track to track across a surface of the disc under the control of electronic circuitry. The discs are mounted for rotation on a spindle motor which causes the discs to spin and the surface of the discs to pass under the heads.
As magnetic storage densities have increased, magnetic disc drives have been required to operate with increasingly greater precision. This requirement has meant that magnetic recording heads have been placed increasingly close to the surface of the magnetic disc. The interaction between the magnetic head and the recording surface has also become increasingly precise. This has required the environment of the magnetic disc to be free from particulate and liquid contaminants. Typically, the disc environment is sealed during manufacture so that contaminants cannot enter the housing and contact the storage disc or the magnetic recording head. Additionally, it is important that the disc environment within the chassis remain contaminant free following manufacturing and during operation of the disc drive system. Even minute contaminants can have catastrophic results on disc operation. For example, particulate buildup between the transducing head and the disc can cause degradation in the readback signal, head crashes and damage to the disc surface.
One source of particulate and liquid contaminants in the sealed chassis is the disc drive spindle motor which rotates the storage disc. The disc rotates at speeds in excess of several thousands of RPM. The motor is sealed, and the magnetic disc and the rotor which support the magnetic disc are rotatably coupled to a fixed member of the motor, but the seal is not perfect and contaminants tend to escape from the motor into the sealed chassis. The prior art shows a number of attempts to reduce this tendency. For example, U.S. Pat. No. 5,011,165, issued Apr. 30, 1994, to Cap, entitled "SEALING DEVICE ESPECIALLY FOR HARD DISK DRIVES," describes a ferrofluid seal which is used to isolate the environment of the drive motor from the sealed disc environment. The ferrofluid seal is a fluidic seal made of a ferrofluid which is held in place by a magnet. The fluid extends across a gap between a fixed portion of the disc drive motor and the rotor, and thereby prevents contaminants from the motor from entering the sealed environment. However, one problem with the ferrofluid seal is that the ferrofluid may tend to leak from the seal and enter the disc environment which leads to the problems discussed above. Further, fluid from the ferrofluid seal may leak into the motor which may cause damage. Additionally, leakage of ferrofluid reduces the effective quantity of ferrofluid in the seal thereby reducing the effectiveness of the seal.
Another type of seal is a "labyrinth" seal. Typically, a labyrinth seal is a small gap at a small diameter of the motor which extends over a long path. This arrangement tends to inhibit contaminants from the motor from escaping through labyrinth into the sealed disc environment. It can be seen that the labyrinth seal can be made more effective by reducing the gap and lengthening the path. However, this requires precision machining which is both difficult, time consuming and expensive. Although labyrinth seals tend to be less expensive than ferrofluid seals, labyrinth seals are typically not as effective in isolating the motor from the disc environment. Further, some of ferrofluid in a ferrofluid seal may leak from the region of the magnet.
There is a continual need for improving the isolation between the motor and the contaminant-free disc environment.